A. Another possibility is that this lesion is something called an eosinophilic plaque. These are often allergy-related, and appear as scabs on the head (and sometimes other areas, but very frequently we see them on the face and head) of cats. Often they will improve with a change to a hypoallergenic diet, but many times cats need steroid drugs to reduce the immune system's reaction, which is what's causing the lesion. Unfortunately it takes a biopsy to tell the difference between an eosinophilic plaque and cancer, and since cancer is life-threatening this is definitely a procedure I recommend.
A. I doubt it is a parasite, but this can be riled out by doing a skin scraping at the vet. A tumor can also be confirmed by checking a stained slide from this black scab.
If it has defined margins and feels movable above the skin, it would probably be a good idea to have it removed surgically before it becomes too big or attached to the tissue underneath the skin.
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